Active Grubs in June?


A co-worker, Dave Dawson, sent me a picture of a grub that he found in his brother’s lawn while putting in a French drain.

The grub was buried about three or four inches into the soil. He thought it was amazing to see not one, but five or six grubs, while digging a trench about 2 feet long.
The life cycle of an annual white grub is considered a complete metamorphosis. It starts off as an egg, laid from May through July, depending on the species and location. The eggs hatch into larva or grubs and they feed on basically whatever is in front of their mouth. They will feed on soil, roots and other organic matter. After feeding for 6 to 8 weeks, they will dig themselves down into the soil to avoid the cold water.

Once it warms up again in the spring, they will rise just up into the root zone, continue feeding for a while, but not enough to cause any real damage to the growing grass. Then, the grubs will burrow down into the ground, pupate, and turn into an adult. The adult flies around for 4 to 6 weeks, laying eggs during the summer and then the whole process starts again.

We occasionally get lawn care service calls from customers in the spring saying they have grubs and want us to apply an insect control application. The feeding they do in the spring is very light, so they generally do not eat enough of the insect control product to be controlled. Plus, the grass is growing rapidly in the spring, so any roots that are eaten are quickly replaced.

The grubs Dave found were getting ready to pupate into adults. He did find one that was emerging from the pupal case as an adult as well, but before he could get a picture of it, his daughter decided to control it naturally, by squishing it with a rock.

It’s Grub Time!

Grubs are the larval stage of a scarab beetle.  There are at least ten different species of beetles that produce grubs that damage lawns to varying degrees.  About a week ago, I saw the adults of the Masked Chafer, a common beetle in cool season turfgrass areas in the Midwest and Lower Midwest including the Chicago area.  They seem to be out a little earlier than normal this year.  The beetle that seems to cause the most damage is the Japanese beetle as the adults feed on many trees and flowering plants.  The female adult lays her eggs in turf areas, which hatch into lawn damaging grubs.  The Japanese beetle adults will start hatching soon and begin feeding.  In some southern areas, the adults may already be active.

The grubs act like mini sod cutters as they feed on the roots of the grass plant, starting in mid-July and lasting well into fall.  If rain is plentiful, the grass plants can often replace the roots that have been eaten and the damage may go unnoticed.  The bigger problem comes from skunks, raccoons, opossums and even birds that tear up a lawn looking for a tasty meal.  They damage caused by these animals and birds are often far worse than what the actual grub will cause.

The best defense is to apply a preventative grub control now, before the eggs hatch, to prevent them from becoming a problem.  The insect control material has to be watered in well to move it into the soil where the insect can come in contact with it.  If you have had problems with grubs in the past, now is the time to prevent damage later this year.